DE3511456A1 - METHOD AND DEVICES FOR THE PRODUCTION OF GLASS BODIES - Google Patents

Description

Process / for the production of vitreous bodies

The invention relates to a method for the production of glass bodies, in which from the starting material for the Glass body in the form of an anhydrous suspension with a highly dispersed solid content formed a porous green body and this is then cleaned and sintered.

The invention further relates to devices for carrying out such a method and to the use the glass body produced by the method according to the invention.

The method mentioned at the beginning is particularly suitable for producing preforms for optical waveguides made of quartz glass.

For the production of high-purity quartz glass articles, particularly preforms for optical waveguides, methods are known in which a porous green body made of highly disperse SiO2 ~ glass particles is prepared, after which this porous green body is firstly cleaned of a chlorine-containing atmosphere at temperatures in the range of 600 to 900 ⁰ C in for example will. The sintering to compact, transparent glass then takes place at temperatures in the range around 1500 ⁰ C; the level of the sintering temperature depends on the size of the SiO2 particles and the homogeneity of the green body.

The processing of highly dispersed quartz glass particles requires a considerable amount of equipment (preforms for the Manufacture of a manageable green body and pressing for

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required the compaction of this green body), to finally obtain a green body for the efficient sintering, that is, sintering at temperatures ^ - having 1550 ⁰ C to a bubbles and reams free glass body, a sufficient high density. Such a method for producing a preform for optical waveguides is known from DE-PS 32 40 355, for example.

In order to be able to produce green bodies of sufficient density, It is also known to start from highly disperse SiO2 suspensions which are shaped into a green body. the end DE-OS 29 25 309 discloses a method in which an SiO2 suspension is sprayed into or onto a carrier tube will. The disadvantage of this process is that there are high demands on a uniformly operating spray device must be made and that a cleaning of the green body obtained in a binding impurities hot gas atmosphere is not possible because the carrier tube is not porous.

The invention is based on the object of a method and devices for the production of high-purity glass bodies with which a green body is obtained which is porous enough that it is in a reheating step can be cleaned well in a gas atmosphere which reacts with the impurities present, but which has such a high compression that the subsequent sintering step without additional compression measures of the cleaned green body can be done.

This object is achieved with the method according to the invention solved that the green body by separating the phases of the suspension on one, the shape of the to be produced Glass body corresponding deposition electrode is deposited by means of electrophoresis.

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Devices for performing this method are characterized by

1. a vessel to hold the to be separated according to phases Starting material in the form of a suspension with one that Deposition electrode corresponding to the shape of the green body to be produced, which is inserted into the suspension contained in the vessel immersed, with a corresponding in shape and size of the separation electrode, in the vessel at a distance from Separating electrode arranged counter-electrode and with a voltage source, which is connected to the counter-electrode and the Separation electrode is electrically connected via electrode connections

2. a tube corresponding to the shape of the green body to be produced as a deposition electrode with an electrical insulating soil for receiving starting material to be separated according to phases in the form of a suspension, with a immersed in the pipe, to all points of the separation surface equidistant inner electrode as a counter electrode and with a voltage source that is connected to the Inner electrode and is electrically connected to the tube via electrode connections and

3. A vessel for receiving an electrically conductive liquid, in which one of the Form of the green body to be produced corresponding porous membrane is immersed, the pores of a diameter smaller than the mean particle diameter of the solid part of one to be separated into phases in the device Has suspension and in front of its, the separation surface opposite main surface preferably one displaceable electrode is arranged at a distance, with a, protruding into the membrane, displaceable Inlet pipe made of electrically conductive material, through which the suspension can be introduced into the membrane and with a voltage source connected to the inlet pipe and to the electrode, which can be moved over the membrane, via electrode connections is electrically connected.

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According to an advantageous further development of the method according to the invention, a suspension, the SiO ₂ particles, is used as the starting material for the glass body

a diameter of 10 to 500 nm, preferably 15 to 100 nm, with an average particle diameter of 40 nm, the dispersing liquid being an electric weakly conductive, anhydrous liquid, in particular ethanol, is used. For the separation of macropore-free Layers are useful as a dispersing liquid to use an anhydrous, organic liquid. In the case of aqueous suspensions, the problem arises that at the anode not only the negatively charged solid particles, in particular these are quartz glass particles, be deposited, but it will be deposited in the case of voltages> 1V simultaneously releases oxygen, which is also deposited on the anode and thus is built into the growing solid layer and pores within the green body formed in this way leads that are undesirable.

According to further advantageous embodiments of the invention, an ionic, anhydrous additive which shifts the pH of the suspension towards the basic range (pH < 10) is added to the suspension. For this purpose, a quaternary ammonium compound, preferably tetramethylammonium hydroxide (TMAH), is preferably added in an amount of 0.1 to 5% by weight, based on the solids content of the dispersing liquid in the suspension. This additive is highly volatile and can be removed from the green body without residue in a subsequent cleaning / heating step, so that quartz glass bodies of a very high purity can be produced. By adding an ammonium compound, for example TMAH, green bodies of relatively high strength are achieved, since gel formation occurs _{at the contact points between two SiO 2 primary particles.} SiO ₂ is precipitated at the contact points and forms a bridging layer, since SiO _{2 is} slightly soluble in TMAH.

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According to a further advantageous embodiment of the method according to the invention, on the deposition electrode a layered body by depositing several layers one after the other from differently doped suspensions deposited. For this purpose, after a desired layer thickness of the green body has been reached, the first suspension is made from the Device removed and the deposition process doped with a second, e.g. different from the first suspension Suspension continued. The present method is therefore particularly suitable for preforms for optical waveguides produce which have a stepped profile of the refractive index. It is also possible to use an optical Waveguide with W-profile by incorporating an intermediate layer with a lower refractive index, which is achieved by using a suspension with appropriate doping is obtained. Dopants to change the The refractive index of a glass body is known to the person skilled in the art; for example, this is done to increase the refractive index Ge (> 2 or AI2O3 and to lower the refractive index B2O3 or fluorine used. With the present In the process, it is also possible to produce a quartz glass body by depositing a large number of graded layers with an approximately continuous course of the refractive index.

According to a further advantageous embodiment of the method according to the invention, a deposition electrode is used Membrane in the form of a porous green body from the starting material used for the glass body to be produced, wherein the electrophoretic deposition of the solid fraction of the suspension by means of a, in front of the deposition surface opposite main surface of the membrane arranged at a distance, preferably displaceable Electrode is effected. This has the advantage that for the production of preforms for optical waveguide according to the method according to the invention

PHD 85-044

alien materials for the separation electrode can be avoided, which may contaminate the obtained Can lead green body, high-precision optical waveguides are also created in this way can with a stepped profile of the refractive index if different for the membrane and the green body to be deposited doped starting materials are used. Instead of a porous, not yet sintered green body A porous, sintered-on body made from the starting material for the glass body can also be used as the membrane can be used. It is particularly advantageous that layers from the solid content of the suspension with a compared to the grain fraction used for the production of such a membrane produced grain fraction changed can be. The shrinkage behavior of a body depends on the grain fraction; if as a membrane If an already sintered-on body is used from the starting material for the glass body, it is possible to use the Membrane and the layer to be deposited on it to adapt to one another in terms of their shrinkage behavior. With this modification of the method according to the invention, the membrane and the deposited green body are combined in one cleaning step Purified in a suitable heated gas phase and then together to form a transparent one Sintered vitreous.

If, according to an advantageous development of the method according to the invention, the solids content of the suspension is deposited on a thermoplastic and electrically conductive intermediate ^{layer, preferably made of 40% by weight of paraffin with a melting point of 46 to 50 °} C. and 60% by weight of graphite powder ^ , there is the advantage that the green body deposited on the deposition electrode can be removed from the mold particularly easily by heating the deposition electrode. The one with the

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Invention achievable advantages are further in particular that for the production of glass bodies, in particular Preforms for optical waveguides, green bodies can be obtained with very little expenditure on equipment that on the one hand are porous enough to effectively remove impurities in a heated gas atmosphere can be removed, which on the other hand, however, have such a high density and homogeneity that they can be removed without further Intermediate processing steps, such as hot isostatic pressing, can be sintered into high-purity glass bodies can. Another advantage of the method of the present invention is that green bodies can be produced which have a cross section deviating from a circular cross section; think of e.g. angular tubes or rods or hollow bodies of any shape. The deposited green bodies can Dry crack-free and after the cleaning and sintering step result in dimensionally accurate, transparent and high-purity glasses with extremely smooth surfaces.

It is also possible to use quartz glass tubes manufactured in the manner described in the manufacture of halogen or discharge lamps, where also, as well as for green bodies that are used for the production of optical Waveguides to be used require a glass with very low water content and high silicon dioxide content is.

By separating the dispersing liquid from the solid phase of the suspension via electrophoresis forms a relatively dry, solid green body, which is good can be handled and which, without the risk of cracking occurs, in a relatively short time from the small remaining residual moisture can be freed, e.g. by drying under atmospheric conditions or by solvent exchange.

PHD 85-044

Those skilled in the art are familiar with these drying processes.

Embodiments of the invention are shown in the drawing and are described in more detail below. Show it:

Figures 1 and 2 devices for performing the method according to the invention in section for the production of tubular green bodies,
10

Figure 3 device for performing the method according to the invention in section for the production of rod-shaped Green bodies.

In Figure 1, a device for producing a tubular green body 7 is shown. To do this, a E.g. in an ultrasonic field homogenized, anhydrous suspension 5 of highly dispersed SiO2 ~ particles of one diameter in the range from 10 to 500 nm, preferably 15 to 100 nm, with an average particle diameter of 40 nm with an electrically weakly conductive, anhydrous liquid, in particular ethanol, as the dispersing liquid (Solid: dispersing liquid weight ratio 1: 1.5 to 1: 8) containing a quaternary ammonium compound, especially tetramethylammonium hydroxide (TMAH) in an amount from 0.1 to 5% by weight, based on the solids content in the suspension, is added to a vessel 1, in which a counter electrode 3 in the form of a grid electrode is arranged on the wall of the vessel 1. Will continue a separation electrode is arranged in the vessel 1 and thus in the suspension 5 at a distance from the counter electrode 3, which in this example is a cylinder 9 with an outside diameter of 22 mm.

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The separating electrode (cylinder 9) immersed in the suspension 5 is made of electrically conductive, non-metallic material, preferably graphite, and is at the same distance from all points of the counter electrode 3. The deposition electrode in the form of the cylinder 9 is expediently provided with a thermoplastic and electrically conductive layer 13 with a layer thickness of about 1 mm on the deposition surface in order to facilitate the subsequent demolding of the green body 7 deposited on the cylinder 9. The layer 13 is advantageously produced from a material which consists of 40% by weight of paraffin with a melting point of 46 to 50 ^° C. and 60% by weight of graphite powder. To remove a deposited green body, the deposition electrode in the form of the graphite cylinder 9 is heated from the inside, for example by hot water, after which the green body 7 deposited on the layer 13 can easily be removed from the cylinder 9. When an electrical voltage is applied from a voltage source (not shown) to the electrodes 3 and 9 via electrode connections 11, the green body 7 is deposited as a uniformly thick layer. At a voltage of 30V, a current density of about 0.07 μA / cm ^ electrode area resulted; after a deposition time of 15 minutes, the layer thickness of the deposited green body was approximately 1.5 mm.

The distance from the counter electrode 3 to the deposition electrode (cylinder 9) is not critical and does not have any influence even layer growth.

In a practical embodiment using A device according to FIG. 1 was processed as follows: 100 g of commercially available S1O2 of one particle size from 15-100 nm with an average particle diameter of 5 40 nm in 400 ml of ethanol and 4 ml of tetramethylammonium hydroxide (TMAH) dispersed until homogeneous

PHD 85-044

Suspension is reached. Homogenization can be achieved, for example, by coupling an ultrasonic field with a frequency f = 35 kHz into the suspension. This suspension is separated according to phases, as described for FIG. 1, and the green body obtained is slowly dried in air over the course of 24 hours to remove the residual moisture. The green body obtained in this way has a density of 52% of the density of compact quartz glass. The as described above from the deposition electrode removed green body is then heated over a period of 100 min to a temperature of 800 ⁰ C and exposed for removal of contaminants, in particular water, and transition metals, 1.5 h a saturated solution of SOCl 2 02 gas stream. The subsequent sintering is performed at 1500 ⁰ C in a helium atmosphere with 2% by volume chlorine gas addition, wherein the green body is performed with a lowering speed of 3mm / min through the furnace. A transparent glass tube with an outside diameter of 19 mm and a wall thickness of 1.2 mm with impurities <. Get 10 ppb. The glass produced in this way had a density of 2.20 g / cm ^ and a refractive index nu = 1.4598.

According to the method described, it is also possible to produce green bodies with layer structures made of differently doped To generate Si02 ~ suspensions. For this purpose, the suspension is applied after the desired layer thickness has been reached quickly sucked out of the device and replaced by a new, differently doped suspension. Leave that way green bodies form which, after sintering, result in glasses with a refractive index gradient.

In Figure 2, a device is shown with which a tubular green body 7 is also from the suspension 5 can be produced. Here is the electrophoretic deposition of a green body in one, with an electrical one insulating bottom 17 sealed tube 15 as a separation electrode shown. The tube 15 can be made electrically

PHD 85-044

conductive material such as graphite and is expediently coated with a thermoplastic, electrically conductive layer 13, which allows for better demolding of the inside of the pipe used to be deposited green body. The tube 15 can also consist of an electrically insulating material and then has an electrically conductive thermoplastic layer 13 of the above on its deposition surface inside described composition. In the tube 15, an inner electrode 19 is arranged as a counter electrode, which through the bottom 17 is centered. The tube 15 can be in one piece or divided into several parts. When depositing green bodies of larger dimensions, a multi-part tube facilitates demolding.

The suspension used, the deposition conditions as well as the post-processing of the green body obtained as well the properties of the quartz glass body obtained correspond to the example described for FIG.

PHD 85-044

It can be used to produce rod-shaped green bodies 25 can also be proceeded in such a way that a porous body corresponding to the shape of the green body to be produced is placed in a vessel 21 Membrane as a separation electrode in the form of a cylinder 27 with pores of a diameter <the mean particle diameter of the solid particles contained in the suspension, for the described embodiment asof; 40 nm, is introduced, the remote from the deposition surface on their Main surface an electrode in the form of an electrode which can be displaced over this main surface and which surrounds the cylinder 27 Has ring electrode 29 (see Figure 3). The vessel 21 is filled with an electrically conductive liquid 23, for example water, filled. The membrane in the form of the cylinder 27 protrudes in the axial direction of the cylinder 27 displaceable feed pipe 31 into it, via which starting material to be separated according to phases in the form of the suspension 5 can be introduced into the cylinder 27. The feed pipe is made of electrically conductive, preferably non-metallic Material produced and forms the counter electrode to the displaceable ring electrode 29 via the electrode connections 11 are both electrodes with a not shown Voltage source connected. By electrophoretic deposition of the solid content of the suspension 5 can a rod-shaped green body 25 while continuously pulling up the inlet pipe 31 in the direction of the arrows in

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FIG. 3 deposited within the membrane in the form of the cylinder 27 will. The separated liquid phase of the suspension 5 can at the upper end of the device through a overflow pipe, not shown, can be removed from the device.

The suspension used, the deposition conditions such as the post-processing of the green body obtained and the properties of the quartz glass body obtained also correspond also the example described for FIG.

List of reference symbols

1 vessel

3 counter electrode

5 suspension

7 tubular green body

9 Separation electrode in the form of a cylinder

11 electrode connections

13 electrically conductive and / or thermoplastic layer

15 tube

17 electrically insulating floor of

19 inner electrode

21 vessel

23 electrically conductive solution

25 rod-shaped green body

27 membrane in the form of a cylinder

29 ring electrode

31 inlet pipe

Claims (31)

351H56 PHD 85-044 PATENT CLAIMS 1. A process for the production of glass bodies, in which a porous green body is formed from the starting material for the glass body in the form of an anhydrous suspension with highly dispersed pesticide content and this is then cleaned and sintered,
characterized, that the green body by separating the phases of the suspension on one, the shape of the glass body to be produced corresponding deposition electrode is deposited by means of electrophoresis. 2. The method according to claim 1, characterized in that a suspension is used as the starting material for the glass body which contains SiO2 particles with a diameter in the range from 10 to 500 nm, preferably 15 to 100 nm, with an average particle diameter of 40 nm. 3. The method according to claims 1 and 2, characterized in that that the dispersing liquid is an electrically weakly conductive, anhydrous liquid is used. 4. The method according to claim 3, characterized in that ethanol is used as the dispersing liquid. 5. The method according to claims 1 to 4, characterized in that that a suspension with a solids: dispersing liquid weight ratio from 1: 1.5 to 1: 8 is used. PHD 85-044 6. The method according to any one of the preceding claims, characterized in, that an ionic, anhydrous additive is added to the suspension, which increases the pH of the suspension in the direction shifts to the basic range (pH £ 10). 7. The method according to claim 6, characterized in that a quaternary ammonium compound is added as the ionic additive. 8. The method according to claim 7, characterized in that tetramethylammonium hydroxide (TMAH) is used as the ionic additive. 9. The method according to any one of the preceding claims, characterized in, that the ionogenic additive in an amount of 0.1 to 5 wt.%, Based on the solids content in the suspension. 20th 10. The method according to any one of the preceding claims, characterized in, that on the deposition electrode a layered body differs from each other by deposition of several layers one after the other doped suspensions is deposited. 11. The method according to claim 10, characterized in that suspensions are used with dopants which cause different refractive indices of the glass body to be produced. 12. The method according to any one of the preceding claims, characterized in that that a thermoplastic and / or electrically conductive layer is applied to the deposition electrode which the solids content of the suspension is deposited. . 3 · -> 6 - PHD 85-044 13. The method according to any one of the preceding claims, characterized in, that a deposition electrode made of a non-metallic, electrically conductive material is used. 5 14. The method according to claim 13, characterized in that a separation electrode made of graphite is used. 15. The method according to claim 16, characterized in that a deposition electrode made of an electrically insulating material is used. 16. The method according to claim 12, characterized in that a layer of 40 wt.% Paraffin with a melting point of 46 to 50 ⁰ C and 60 wt.% Graphite powder is used. 17. The method according to any one of the preceding claims, characterized in that that a membrane in the form of a porous green body made of the starting material for the to be produced as a separation electrode Glass body is used, with the electrophoretic deposition of the solid content of the suspension by means of a, in front of the main surface of the membrane opposite the separation surface at a distance, preferably displaceable electrode is effected. 18. The method according to any one of the preceding claims, characterized in, that the solids content of the suspension is deposited on the deposition electrode at a current density of 0.01 to 100 μA / cm ^{2 electrode area.} 3511458 - γΐ - PHD 85-044 19. Device for performing the method according to claims 1 to 18, characterized by a vessel (1) for Absorption of starting material to be separated according to phases in the form of a suspension (5), with one of the shape of the one to be produced Deposition electrode corresponding to the green body, which is immersed in the suspension contained in the vessel one corresponding in shape and size to the separation electrode, in the vessel at a distance from the separation electrode arranged counter-electrode (3) and with a voltage source connected to the counter-electrode and the separation electrode is electrically connected via electrode connections (11). 20. Apparatus according to claim 19,
characterized, that the deposition electrode is a cylinder (9) on which a tubular green body (7) can be deposited. 21. Device for performing the method according to claims 1 to 18, characterized by a tube (15) corresponding to the shape of the green body to be produced as a deposition electrode with an electrical insulating base (17) for receiving starting material to be separated according to phases in the form of a suspension (5), with an inner electrode (19) which is immersed in the tube and is equidistant to all points on the deposition surface Counter electrode and with a voltage source connected to the inner electrode and to the tube via electrode connections (11) is electrically connected. PHD 85-044 22. Device for performing the method according to claims 1 to 18, characterized by a vessel (21) for receiving an electrically conductive liquid (23), in which one of the shape of the to be produced as a separation electrode Green body corresponding porous membrane is immersed, the pores of a diameter smaller than that mean particle diameter of the solids content of a in the device according to phases to be separated suspension (5) and in front of it, the separation surface opposite Main surface, a preferably displaceable electrode is arranged at a distance, with a, in the membrane protruding, displaceable inlet pipe (31) made of electrically conductive material, via which the Suspension can be introduced into the membrane and with a voltage source connected to the inlet pipe and to the over the membrane-displaceable electrode via electrode connections (11) is electrically connected. 23. The device according to claim 22, characterized in that the membrane is a cylinder (27) in which a rod-shaped green body (25) can be deposited by moving a ring electrode (29) surrounding the membrane in the axial direction. 24. Device according to claims 22 and 23, characterized in that that the membrane is a porous green body from the starting material for the glass body to be produced. 25. Device according to claims 19 to 21, characterized in that that the separation electrode (9, 15) on the separation surface with a thermoplastic and / or electrical conductive layer (13) is provided. - y> - PHD 85-044 26. The device according to claim 25, characterized in that the layer consists of 40% by weight of paraffin with a melting point of 46 to 50 ^° C. and 60% by weight of graphite powder. 27. Device according to claims 25 and 26, characterized in that that the separation electrode (9, 15) consists of a non-metallic, electrically conductive material. 28. The device according to claim 27, characterized in that the separation electrode (9, 15) consists of graphite. 29. Device according to claims 25 and 26, characterized in that that the separation electrode (9, 15) consists of an electrically insulating material. 30. Use of glass bodies produced by the method according to claims 1 to 18 as a preform for optisehe Waveguide. 31. Use of glass bodies produced by the method according to claims 1 to 18 for lamp bulbs, in particular of halogen or gas discharge lamps.